在Java filter中调用service层方法

Posted 2020-08-08 天外有天2013

在项目中遇到一个问题，在 Filter中注入 Serivce失败，注入的service始终为null。如下所示：

 1 public class WeiXinFilter implements Filter{
 2     
 3     @Autowired
 4     private UsersService usersService;
 5 
 6     public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
 7         HttpServletRequest req = (HttpServletRequest)request;
 8         HttpServletResponse resp = (HttpServletResponse)response;
 9 　　　　 Users users = this.usersService.queryByOpenid(openid);
10 }

上面的 usersService 会报空指针异常。

解决方法一：

 1 public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
 2         HttpServletRequest req = (HttpServletRequest)request;
 3         HttpServletResponse resp = (HttpServletResponse)response;
 4         ServletContext sc = req.getSession().getServletContext();
 5         XmlWebApplicationContext cxt = (XmlWebApplicationContext)WebApplicationContextUtils.getWebApplicationContext(sc);
 6         
 7         if(cxt != null && cxt.getBean("usersService") != null && usersService == null)
 8             usersService = (UsersService) cxt.getBean("usersService");
 9         
10         Users users = this.usersService.queryByOpenid(openid);

解决方法二：

public class WeiXinFilter implements Filter{
    
    private UsersService usersService;
    
    public void init(FilterConfig fConfig) throws ServletException {
        ServletContext sc = fConfig.getServletContext(); 
        XmlWebApplicationContext cxt = (XmlWebApplicationContext)WebApplicationContextUtils.getWebApplicationContext(sc);
        
        if(cxt != null && cxt.getBean("usersService") != null && usersService == null)
            usersService = (UsersService) cxt.getBean("usersService");        
    }

相关原理：

1. 如何获取 ServletContext：

1）在javax.servlet.Filter中直接获取
ServletContext context = config.getServletContext();

2）在HttpServlet中直接获取
this.getServletContext()

3）在其他方法中，通过HttpServletRequest获得
request.getSession().getServletContext();

2. WebApplicationContext 与 ServletContext (转自：http://blessht.iteye.com/blog/2121845)：

Spring的 ContextLoaderListener是一个实现了ServletContextListener接口的监听器，在启动项目时会触发contextInitialized方法（该方法主要完成ApplicationContext对象的创建），在关闭项目时会触发contextDestroyed方法（该方法会执行ApplicationContext清理操作）。

ConextLoaderListener加载Spring上下文的过程

①启动项目时触发contextInitialized方法，该方法就做一件事：通过父类contextLoader的initWebApplicationContext方法创建Spring上下文对象。

②initWebApplicationContext方法做了三件事：创建 WebApplicationContext；加载对应的Spring文件创建里面的Bean实例；将WebApplicationContext放入 ServletContext（就是Java Web的全局变量）中。

③createWebApplicationContext创建上下文对象，支持用户自定义的上下文对象，但必须继承自ConfigurableWebApplicationContext，而Spring MVC默认使用ConfigurableWebApplicationContext作为ApplicationContext（它仅仅是一个接口）的实 现。

④configureAndRefreshWebApplicationContext方法用 于封装ApplicationContext数据并且初始化所有相关Bean对象。它会从web.xml中读取名为 contextConfigLocation的配置，这就是spring xml数据源设置，然后放到ApplicationContext中，最后调用传说中的refresh方法执行所有Java对象的创建。

⑤完成ApplicationContext创建之后就是将其放入ServletContext中，注意它存储的key值常量。

解决方法三：

直接使用spring mvc中的HandlerInterceptor或者HandlerInterceptorAdapter 来替换Filter:

public class WeiXinInterceptor implements HandlerInterceptor {
    @Autowired
    private UsersService usersService;   
    
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        // TODO Auto-generated method stub
        return false;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView)
            throws Exception {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        // TODO Auto-generated method stub
        
    }
}

配置拦截路径：

    <mvc:interceptors>
        <mvc:interceptor>
            <mvc:mapping path="/**" />
            <bean class="net.xxxx.interceptor.WeiXinInterceptor" />
        </mvc:interceptor>     
    </mvc:interceptors>

Filter 中注入 Service 的示例：

 1 public class WeiXinFilter implements Filter{    
 2     private UsersService usersService;    
 3     public void init(FilterConfig fConfig) throws ServletException {}
 4     public WeiXinFilter() {}
 5     public void destroy() {}
 6 
 7     public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
 8         HttpServletRequest req = (HttpServletRequest)request;
 9         HttpServletResponse resp = (HttpServletResponse)response;
10         
11         String userAgent = req.getHeader("user-agent");
12         if(userAgent != null && userAgent.toLowerCase().indexOf("micromessenger") != -1){    // 微信浏览器
13             String servletPath = req.getServletPath();
14             String requestURL = req.getRequestURL().toString();
15             String queryString = req.getQueryString();
16  
17             if(queryString != null){
18                 if(requestURL.indexOf("mtzs.html") !=-1 && queryString.indexOf("LLFlag")!=-1){
19                     req.getSession().setAttribute("LLFlag", "1");
20                     chain.doFilter(request, response);
21                     return;
22                 }
23             }
24             
25             String openidDES = CookieUtil.getValueByName("openid", req);
26             String openid = null;
27             if(StringUtils.isNotBlank(openidDES)){
28                 try {
29                     openid = DesUtil.decrypt(openidDES, "rxxxxxxxxxde");    // 解密获得openid
30                 } catch (Exception e) {
31                     e.printStackTrace();
32                 }    
33             }
34             // ... ...
35             String[] pathArray = {"/weixin/enterAppFromWeiXin.json", "/weixin/getWeiXinUserInfo.json",
36                                     "/weixin/getAccessTokenAndOpenid.json", "/sendRegCode.json", "/register.json", 
37                                     "/login.json", "/logon.json", "/dump.json", "/queryInfo.json"};
38             List<String> pathList = Arrays.asList(pathArray);
39             
40             String loginSuccessUrl = req.getParameter("path");
41             String fullLoginSuccessUrl = "http://www.axxxxxxx.cn/pc/";
42             if(requestURL.indexOf("weixin_gate.html") != -1){
43                 req.getSession().setAttribute("loginSuccessUrl", loginSuccessUrl);
44 　　　　　　　　　　// ... ...
45             }
46             ServletContext sc = req.getSession().getServletContext();
47 XmlWebApplicationContext cxt = (XmlWebApplicationContext)WebApplicationContextUtils.getWebApplicationContext(sc);
48         
49             if(cxt != null && cxt.getBean("usersService") != null && usersService == null)
50                usersService = (UsersService) cxt.getBean("usersService");
51         
52             Users users = this.usersService.queryByOpenid(openid);
53             // ... ...
54             if(pathList.contains(servletPath)){    // pathList 中的访问路径直接 pass 
55                 chain.doFilter(request, response);
56                 return;
57             }else{
58                 if(req.getSession().getAttribute(CommonConstants.SESSION_KEY_USER) == null){ // 未登录
59                     String llFlag = (String) req.getSession().getAttribute("LLFlag");
60                     if(llFlag != null && llFlag.equals("1")){    // 处理游客浏览
61                         chain.doFilter(request, response);
62                         return;
63                     }                  
64                     // ... ...// 3. 从腾讯服务器去获得微信的 openid ,
65                     req.getRequestDispatcher("/weixin_gate.html").forward(request, response);
66                     return;
67                 }else{    // 已经登录
68                     // 4. 已经登录时的处理                    
69                     chain.doFilter(request, response); 
70                     return;
71                 }
72             }            
73         }else{    // 非微信浏览器
74             chain.doFilter(request, response);
75         }
76     }
77 
78 }